Barfod, Anders S.6; Hagen, Melanie7; Borchsenius, Finn8
1 Department of Bioscience - Ecoinformatics and Biodiversity, Department of Bioscience, Science and Technology, Aarhus University2 Department of Bioscience - Genetics, Ecology and Evolution, Department of Bioscience, Science and Technology, Aarhus University3 Science Museums - The Herbarium, Science Museums, Science and Technology, Aarhus University4 Science Museums, Science and Technology, Aarhus University5 Dean's Office, Science and Technology, Science and Technology, Aarhus University6 Department of Bioscience - Ecoinformatics and Biodiversity, Department of Bioscience, Science and Technology, Aarhus University7 Department of Bioscience - Genetics, Ecology and Evolution, Department of Bioscience, Science and Technology, Aarhus University8 Dean's Office, Science and Technology, Science and Technology, Aarhus University
More than 60 pollination ecological studies have been conducted on palms since Henderson’s almost 25 year old review of palm pollination. Most studies are aut-ecological studies that provide a detailed snapshot of the pollination of a limited number of palm individuals of the same species. They confirm that most palm inflorescences offer a loose framework for the interaction between the palms and their insect visitors. The pollinators are typically weevils (superfamily Curculionidea), rove beetles (family Staphylinidae), sweat bees (family Halictidae), stingless bees (tribe Meliponini, family Apidae), and flies (order Diptera). Less is known about variations in the composition of the visiting insect fauna across the geographic range of a given palm species. A number canopy studies have contributed to our understanding of palms in broader palm-pollinator networks and provided insight on the specificity of the visiting insects and the temporal variation in their assemblage at a particular species. Preliminary observations in beetle-pollinated palms suggest that insects similar in size, shape and behaviour may substitute for each another both in space and in time. Hence to compare pollination mechanism it might be more useful to distinguish between different functional types of pollinators rather than individual species. There is further evidence that pollination mechanisms differ between palm individuals of the same species growing in contrasting habitat for example light open places versus closed forest. The palm inflorescence constitutes the structural and chemical framework within which interaction with the visiting insects take place. By investing in protective features such as sclerenchyme, raphide-containing ideoblasts and tannin rich tissues the palm may prevent destructive activities of the visiting insects. Adaptation to any pollination mechanism involves a trade-off between the damages caused by the visiting insects and the services rendered by the pollinators. Comparative studies of closely related species have provided valuable insight into transitions in floral morphology as adaptation to diverging pollination mechanisms. Future pollination studies should focus on the dynamics of palm-pollinator interactions including comparative studies in groups where transitions in pollination mechanism may be predicted from differences in floral morphology and phenology. Reconstructions of pollination ecological traits on dated phylogenies will undoubtedly contribute to our knowledge of the evolution of pollination mechanisms as well. This approach is, however, sensitive to correct homology assessments and thus relies on detailed studies of floral development and gene expression.